Rotor device



M r h 21, 1961 H. R. NILSSON 2,975,963

ROTOR DEVICE Filed Feb. 25, 1959 2 Sheets-Sheet 1 IN VEN TOR.

NILSSON, HANS ROBERT March 21, 1961 H. R. NILSSON 2,975,963

ROTOR DEVICE Filed Feb. 25, 1959 2 Sheets-Sheet 2 IN VEN TOR.

NILSSON, HANS ROBERT ROTOR DEVICE Hans Robert Nilsson, Ektorp, Sweden, assignor to Svenska Rotor Maskiner Aktiebolag, Nacka, Sweden, a corporation of Sweden Filed Feb. 25, 1959, Ser. No. 795,534

Claims priority, application Sweden Feb. 27, 1958 7 Claims. (Cl. 230-143) The present invention relates to a rotor device operating with at least two pressure stages and provided with male and female rotors, each one consisting of male and female sections corresponding to the number of stages. The male rotors are provided with helical convex lands and intermediate grooves and the female rotors are provided with helical concave lands and intermediate grooves.

This rotor device is particularly intended for compression or expansion of gaseous media in several stages.

A characteristic feature of the present invention is that the cross section of the male rotor sections show a common basic profile and that likewise the cross sections of the female rotor sections show a common basic profile. Furthermore, the lands of the female sections are, in a lower pressure stage, provided with addendum portions outside the profile of the lands of the female section in the next higher pressure stage, the grooves of the corresponding male section being provided with recesses or dedendums in their bottoms corresponding to these addendum portions in order to obtain a suction volume corresponding to the gas pressure.

Further it is advantageous for a device operating in two stages that the female section of the second stage, i.e. the stage with higher pressure, shows a basic profile without addendum portions and that the male section shows a basic profile without bottom recesses or dedendums.

Further it is advantageous that the sections of the respective rotor show the same land or lobe angle.

Another characteristic feature of the invention is that the addendum portions of the female section are located outside the pitch circle of the female section and that the recesses in the grooves of the male section corresponding to these addendum portions are located inside the pitch .circle of the male section.

The invention is further characterized in that in each rotor the sections show the same pitch diameter.

In a preferred structural arrangement of the rotary device respective rotor consists of integral rotor sections so that each rotor can be journalled only at its outer ends while the sections of said rotor are mutually sealed. In a further preferable arrangement the male rotor is fourthreaded and has a wrap angle for its lands in respective stage below 360. In the low pressure stage, such wrap angle can be lying within the limits 275-325 and preferably be maximum 300". In the high pressure stage such wrap angle can be lying within the limits l50-l90 and preferably be minimum 170.

The ratio or relation between rotor length and rotor diameter is in the low pressure stage preferably lying be tween 1.1 and 1.4 and in the high pressure stage between 0.6 and 0.8 and preferably said relation can be about 1.25 and 0.7 in respective stage.

In a four-threaded male rotor it is further advantageous to make the slide rotor six-threaded.

It is further advantageous that the land profiles of the male sections respectively the groove profiles of the female sections are formed by corresponding equal circular arcs in the two stages and that the addendum por- 2,975,963 Patented Mar. 21, 1961 ice.

tions of the side section and the recesses of the male section show profiles likewise formed by circular arcs.

A further characteristic feature of the invention is that the male and female rotors run with a clearance against each other, which clearance at full meshing between male land and female groove preferably is 0.08-0.1'1 mm. in both the low pressure section and the high pressure sectiori and that the rotors have a common synchronising gear for their rotor sections.

It is further advantageous in a two stage device operating as a compressor to arrange between the low pressure stage and the high pressure stage a cooler for the working medium.

In the accompanying drawings:

Fig. 1 sows a vertical central longitudinal section through a compressor designed according to the invention.

Fig. 2 shows the compressor rotors in a horizontal longitudinal section through the compressor in Fig. 1.

Fig. 3 shows a transverse section through the rotors in the high pressure side taken on the line '3-3 in Fig. 1.

Fig. 4 shows transverse section through the low pressure rotors taken on the line 4-4 in Fig. 1.

Fig. 1 shows a two stage compressor. This compressor has a housing consisting of a 'low pressure end 10, an upper shell 12, a lower shell 14 and a high pressure end 16. A low-pressure inlet 18 is arranged in the low pressure end 10 and in the lower shell 14. In the same manner an intermediate pressure outlet 20 is arranged in the upper shell 12, an intermediate pressure inlet 22 is arranged in the lower shell 14, and a high pressure outlet 24 is arranged in the upper shell 12 and in the high pressure end 16. The upper and lower shells 12 and 14 encircles two working chambers each consisting of two intersecting cylindrical borings in which are arranged a male rotor 26 and a female rotor 28. These rotors are journalled in the low pressure and high pressure ends 10 and 16 and each consists of a low pressure section 30 and 34, respectively, and a high pressure section 32 and 36, respectively, with a smooth intermediate shaft portions 38 and 40, respectively, arranged as to seal against the upper and the lower shells 12 and 14. The high pressure section 32 of the male rotor 26 comprises four helical convex lands 42 located mainly outside the pitch circle of the male rotor44 and the intermediate grooves 46. The high pressure section 36 of the female rotor 28 comprises six helical concave lands located mainly inside the pitch circle 50 of the female rotor and the intermediate grooves 52. The low pressure section of the male rotor 26 comprises likewise four helical concex lands 54 located mainly outside the pitch circle 44 of the male rotor and the intermediate grooves 56 of which each one, however, is provided with a recess 58 inside the pitch circle 44. The low pressure section 34 of the female rotor 28 comprises six helical, substantially concave lands 60 located mainly inside the pitch circle 50 of the female rotor and provided with addendum portions '62 outside the pitch circle 50 and the intermediate grooves 64.

The cross sections of the male rotor 26 in the low pressure section 30 and the high pressure section 32 are identical except for the recesses 58 in the groove bottoms in the low pressure section. In the same way 7 the cross sections of the female rotor 28 in the low pressure section 34 and the high pressure section 36 are identical except for the addendum portions 62 on the rotor lands in the low pressure section. Further, the pitch angle is the same on both sections of the same rotor. Hereby a simplification of the manufacture of the rotor is obtained, because the same feeding and even the same tools can be used for both sections of the same rotor. Because of such arrangement the manufacture of the rotorscan be considerably simplified and cheapened. In order to obtain highest possible efficiency the male rotor is furthermore designed in such a way that in the low pressure section the wrap angle for each land is about 300 and the ratio between section length and section diameter is about 1.25 and in the high pressure section the wrap angle for each land is about 170 and the ratio between section length and section diameter is about 0.7.

Further, the rotors are designed with land profiles even in the addendum portions and recesses substantially consisting of circular arcs which are equal on the male and the female rotors, except for a little difierence for providing a clearance of 0.080.11 mm. between the rotors in the low pressure section as well as in the high pressure'section, in order to prevent direct meshing between these and therefrom arising risk for seizing. Of the rotors only the male rotor is direct driven from a motor shaft, whereas the female rotor, in a manner known per se for compressors of the present type, is driven by the male rotor by means of an additional synchronizing gearing.

The compressor operates in the following manner. Low pressure gas is suctioned-in through the low pressure inlet 18 and is being compressed to an intermediate pressure in the low pressure section 30, 34 and is blown out through the intermediate pressure outlet 20. The gas is thereupon suctioned-in through the intermediate pressure inlet 22 in the high pressure section 32, 36 and is therein further compressed to high pressure gas before it is blown out through the high pressure outlet 24. By designing the rotor sections 30, 32 and 34, 36 respectively, with different cross sections, one and the same weight quantity of gas may be worked upon continuously in the two stages in spite of that the volume quantity varies with the pressure and the temperature, and in spite of that the angle of the rotor lands is the same in the two stages. The size of the addendum portions 52 and the recesses 58 preferably is dimensioned in such a way that the two compressor stages operate with the same weight quantity of gas per time unit, so that no special accumulating vessel between the two pressure stages is necessary. On the other hand, a builtup with an intermediate cooler between the two pressure stages may be advantageous in other forms of constructions. However, consideration must then be taken to such cooling-down at the dimensioning of the addendum portions and the recesses.

The invention is not limited to the shown embodiment but comprises all structural arrangements lying within the scope of the accompanying claims.

What is claimed:

l. Rotor device operating with at least two pressure stages and provided with male and female rotors each one comprising male and female sections corresponding to the number of stages, the male sections being provided with helical convex lands and intermediate grooves and the female sections with helical concave lands and intermediate grooves, the cross sections of the male sections having a common basic profile and the cross sections of the female sections having a common basic profile, and in a lower pressure stage the lands of the female section being provided with addendum portions outside the profile of the lands of the adjacent female section, the grooves of the corresponding male section being provided with recesses in their bottoms corresponding to these addendum portions, similar sections of each pressure stage having the same land angle.

2. Rotor device according to claim 1 having two stages, female section of the second higher pressure stage having a profile with lands substantially on its pitch circle and the male section having a profile with grooves adjacent the inside of its pitch circle.

3. Rotor device according to claim 1 the sections of each rotor having the same pitch diameter.

4. Rotor device according to claim 1 each rotor comprising integral rotor sections.

5. Rotor device according to claim 1 the male and female rotors run with a clearance therebetween, which clearance at full meshing between male lands and female grooves preferably is 0.08-0.11 mm. in both the high pressure and low pressure sections, and that the said rotors have a common synchronizing gear for their rotor sections.

6. A rotor device according to claim 1 the wrap angle for the lands of the low pressure stage of the male rotor lying within the limits 275-325, the wrap angle for the lands of the high pressure stage of the male rotor lying within the limits ISO-, the ratio between rotor length and rotor diameter in the low pressure stage lying between 1.1 and 1.4 and in the high pressure stage between 0.6 and 0.8.

7. A rotor device according to claim 1, the male sections having the same external diameter.

References Cited in the file of this patent UNITED STATES PATENTS 

